Given the fact that electric arcs or sparks were the first means for wireless communication, it may be surprising that there persisted a need for detecting a spectrum of radio frequencies in radio frequency noise, such as generated by an electric arc in an electric circuit. However, such a persisting need has been particularly emphasized by electrical fires and other serious damage caused by accidental arcs in electric power supply systems and other circuits. In this respect, while fuses and circuit breakers are capable of preventing serious overload conditions, they have been generally ineffective to prevent electrical fires and other damage from accidental arcs and sparks which frequently occur and persist at current levels below the level at which the fuse will blow or the circuit breaker has been set to trip.
On the other hand, electrical fault detection has been practiced for a long time. For instance, U.S. Pat. No. 1,462,053, by H. M. Stoller, issued Jul. 17, 1923, and 3,308,345 by A. R. Van Cortlandt Warrington, issued Mar. 7, 1967, show different uses of resonant circuitry for fault detection. U.S. Pat. No. 3,728,620, by J. L. Heins, issued Apr. 17, 1973, constitutes the transmission line as a resonant circuit for fault indication and location, utilizing a variable frequency source coupled to one end of the line. U.S. Pat. No. 3,751,606, by C. W. Kaiser, Jr., issued Aug. 7, 1973, and 3,904,839, and 4,229,626, by J. T. Peoples, issued Sep. 9, 1975 and Oct. 21, 1980, respectively, disclose loop fault locators using demodulators, phase comparators, and other electronic circuits.
U.S. Pat. No. 4,006,410, by D. R. Roberts, issued Feb. 1, 1977, proposed pinpointing the location of corona discharges in an electrical system by processing only those high-frequency components that do not propagate along the wires of the system. U.S. Pat. No. 4,466,071, by B. D. Russell, Jr., issued Aug. 14, 1984, disclosed high impedance fault detection apparatus and methods using a microcomputer system. U.S. Pat. No. 4,543,524 by R. M. Bulley, issued Sep. 24, 1985, may be noted as of interest in the spectrum analyzer area.
Despite this wealth of information and prior proposals, electrical fires and other damage caused by arcs and sparks have continued to devastate electric power supply and other systems, as well as buildings housing them and forests and neighborhoods in which they are located.
Also, vulnerability to false alarms has been a discouraging problem, inasmuch as switching transients, emissions from radio and television transmitters and other sources can easily trigger false alarms in arc detectors.
In another vein, machinery, circuitry, and apparatus often break down and become damaged in a manner or to an extent that could have been prevented if there had been an early detection of unusual arcing. For instance, commutators of electric motors are often damaged when their carbon brushes wear out, since the metallic brush holder springs then rub against the commutator. Since such wear is accompanied by heavy arcing, an early detection of such arcing could signal the need for preventive action. This is, of course, only a representative example of fields where reliable arc detection could be useful.